4 ms·

Propfans are great in theory; extra efficiency! More power! Less weight! However in practice, things are not so rosy. The biggest downsides to propfans are Nois

Propfans are great in theory; extra efficiency! More power! Less weight! However in practice, things are not so rosy. The biggest downsides to propfans are Noise and Safety. Propfans are LOUD! Much louder than the current generation of turbofans. The lack of a fan-case means the tips of the blades are whirling right next to the passenger compartment. Which leads to safety; there's no fan-case to protect the passengers if one of the blades were to detach from the engine. Turbofans all have very stout fan-cases (they're the single heaviest part of all turbofan engines) and the certification processes include a blade-off test to make sure that the case can contain it. A blade puncturing the fuselage would be a big problem.

boarnoah 7y ago
How does the blade detach scenarios differ from turboprops in this case?
- marcosdumay 7y ago
  Props are way slower moving and more resistant to breaking up than fans.
  - aidenn0 7y ago
    They also have far fewer blades.
xhkkffbf 7y ago
Let's just make the props out of some material like safety glass. If it fan hits the s*&t, the blade shatters. I suppose this might make things more catastrophic than they are already, but we're talking about these rare cases when a blade detaches. It's not a good moment.
okcando 7y ago
Would it be impractical to engineer a limited portion of the fuselage to withstand this scenario?
LargoLasskhyfv 7y ago
Then duct them with a ring around them, and some sort of fins/chevrons like the [1] https://duckduckgo.com/?q=CFM+International+LEAP+chevrons&t=ffsb&iar=images&iax=images&ia=images https://duckduckgo.com/?q=CFM+International+LEAP+chevrons&t=... or something like [2] https://en.wikipedia.org/wiki/Ducted_fan https://en.wikipedia.org/wiki/Ducted_fan Furthermore i don't hear much difference between a Cessna 525A CitationJet CJ4 and a Piaggio P.180 Avanti at about a mile of distance, except the Piaggio has more of a buzzing/sawtoothy sound, and the CJ4 more howling. Or take helicopters, an old Bell UH1(D) and a (meanwhile) not so new either Eurocopter 135 are worlds apart. The Bell UH1 a very loud 'carpet beater', the EC 135 almost unbelievably silent in comparison. I mention that because i have fresh memories from one gliding over my roof and balcony into a parking spacee in front of a supermarket in SAR/MEDEVAC role recently. And i'm not deaf either, because i can hear an A380 going from Paris to Shanghai at 11km/950kph trough closed windows with double paned glass in the silence of the night. Anyways, don't be so unimaginative, there are options!
aylmao 7y ago
The location where a fan could hit the fuselage at dangerous speeds is probably well concealed no? As in, once spinning it's probably feasible that the fan hit the fuselage on the back, in the area right next to the fans, but unlikely that it hits on the front, near the cockpit, far from the fan. I wonder if it could be an effective strategy to re-enforce the parts of fuselage that could be hit instead of encasing the fans themselves.

boarnoah 7y ago

How does the blade detach scenarios differ from turboprops in this case?

marcosdumay 7y ago
Props are way slower moving and more resistant to breaking up than fans.
- aidenn0 7y ago
  They also have far fewer blades.

xhkkffbf 7y ago

Let's just make the props out of some material like safety glass. If it fan hits the s*&t, the blade shatters. I suppose this might make things more catastrophic than they are already, but we're talking about these rare cases when a blade detaches. It's not a good moment.

okcando 7y ago

Would it be impractical to engineer a limited portion of the fuselage to withstand this scenario?

LargoLasskhyfv 7y ago

Then duct them with a ring around them, and some sort of fins/chevrons like the [1] https://duckduckgo.com/?q=CFM+International+LEAP+chevrons&t=ffsb&iar=images&iax=images&ia=images https://duckduckgo.com/?q=CFM+International+LEAP+chevrons&t=... or something like [2] https://en.wikipedia.org/wiki/Ducted_fan https://en.wikipedia.org/wiki/Ducted_fan Furthermore i don't hear much difference between a Cessna 525A CitationJet CJ4 and a Piaggio P.180 Avanti at about a mile of distance, except the Piaggio has more of a buzzing/sawtoothy sound, and the CJ4 more howling. Or take helicopters, an old Bell UH1(D) and a (meanwhile) not so new either Eurocopter 135 are worlds apart. The Bell UH1 a very loud 'carpet beater', the EC 135 almost unbelievably silent in comparison. I mention that because i have fresh memories from one gliding over my roof and balcony into a parking spacee in front of a supermarket in SAR/MEDEVAC role recently. And i'm not deaf either, because i can hear an A380 going from Paris to Shanghai at 11km/950kph trough closed windows with double paned glass in the silence of the night. Anyways, don't be so unimaginative, there are options!

aylmao 7y ago

The location where a fan could hit the fuselage at dangerous speeds is probably well concealed no? As in, once spinning it's probably feasible that the fan hit the fuselage on the back, in the area right next to the fans, but unlikely that it hits on the front, near the cockpit, far from the fan. I wonder if it could be an effective strategy to re-enforce the parts of fuselage that could be hit instead of encasing the fans themselves.